Shanghai has closed all live poultry markets in the city and culled more than 20,000 birds to curb the spread of the H7N9 flu virus, which has killed six people in China.

The city's government spokesman Xu Wei said its live poultry markets were being shut temporarily for "public safety" purposes, and all trade in live poultry banned.

The move comes after the virus was found in pigeon samples from Huhuai market in Shanghai, where Xinhua news agency said a total of 20,536 chickens, ducks, geese and pigeons had been slaughtered.

Xinhua news agency reported the latest fatality from the new bird flu strain was a 64-year-old farmer who died in Huzhou, in the eastern province of Zhejiang.

He was the second person from Zhejiang to die from the bird flu strain, with the other four fatalities in Shanghai, China's commercial hub.

Officials say the number of confirmed infections has risen to 16 with two new cases in neighbouring Jiangsu, and a seven-year-old girl quarantined in Hong Kong for tests after she returned from Shanghai and showed flu-like symptoms.

Local television showed men in protective clothing and facemasks entering the market in the city's western suburbs during the night, and dozens of empty birdcages.

On Friday, the entrance to the poultry section was concealed with wooden boards and sealed off with plastic tape, with a police car parked nearby and white disinfectant powder sprinkled in the street.

Two staff members at the market said the slaughter was completed overnight, but one added: "Of course, I'm worried."

Consumers in the city snapped up banlangen, a traditional Chinese medicine for colds made from the roots of the woad plant, used as a blue dye from ancient times.

"We sold out. People are buying it one after another. Everyone is afraid of bird flu," an employee at the SPH drugstore in downtown Shanghai said.

Earlier, the World Health Organization (WHO) played down fears over the H7N9 strain, saying there was no evidence of human-to-human transmission, but that it was crucial to find out how the virus infects humans.

"We have no sign of any epidemiological linkage between the confirmed cases and we have no sign of sustained human-to-human transmission," WHO spokesman Gregory Hartl said.

"The 400 contacts are being followed up to see if any of them do have the virus, have had it from someone else."

Like the H5N1 variant, which typically spreads from birds to humans through direct contact, experts fear the virus could mutate into a form easily transmissible between humans, with the potential to trigger a pandemic.

According to the WHO, the animal source of the infection and its mode of transmission are not yet clear.

"We do not yet know enough about these infections to determine whether there is a significant risk of community spread," the UN's health agency said.

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